Pulse oximetry sensor adaptor

ABSTRACT

An adapter allows the interconnection of a sensor originating from one manufacturer to be coupled with conventionally incompatible monitors originating from other manufacturers to form a properly functioning pulse oximetry system. The adapter matches a sensor driver in a monitor to the current requirements and light source configuration of a sensor. The adapter also matches a sensor&#39;s light detector signal level to the dynamic range requirements of a monitor preamplifier. Further, the adapter provides compatible sensor calibration, sensor type and security information to a monitor. The adapter may have a self-contained power source or it may derive power from the monitor, allowing both passive and active adapter components. The adapter is particular suited as an adapter cable, replacing a conventional patient cable or sensor cable as the interconnection between a sensor to a monitor in a pulse oximetry system.

RELATED APPLICATION

[0001] This is a continuation application based on application Ser. No.09/982,453, filed Oct. 17, 2001, which is a divisional of applicationSer. No. 09/404,060, filed Sep. 23, 1999, now U.S. Pat. No. 6,349,228,which is a continuation of application Ser. No. 09/021,957, filed onFeb. 11, 1998, now U.S. Pat. No. 5,995,855, the entirety of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] Oximetry is the measurement of the oxygen status of blood. Earlydetection of low blood oxygen is critical in the medical field, forexample in critical care and surgical applications, because aninsufficient supply of oxygen can result in brain damage and death in amatter of minutes. Pulse oximetry is a widely accepted noninvasiveprocedure for measuring the oxygen saturation level of arterial blood,an indicator of oxygen supply. A pulse oximetry system consists of asensor attached to a patient, a monitor, and a cable connecting thesensor and monitor.

[0003] Conventionally, a pulse oximetry sensor has both red and infraredLED emitters and a photodiode detector. The sensor is typically attachedto an adult patient's finger or an infant patient's foot. For a finger,the sensor is configured so that the emitters project light through thefingernail and into the blood vessels and capillaries underneath. Thephotodiode is positioned at the finger tip opposite the fingernail so asto detect the LED emitted light as it emerges from the finger tissues.

[0004] The pulse oximetry monitor determines oxygen saturation bycomputing the differential absorption by arterial blood of the twowavelengths emitted by the sensor. The monitor alternately activates thesensor LED emitters and reads the resulting current generated by thephotodiode detector. This current is proportional to the intensity ofthe detected light. A ratio of detected red and infrared intensities iscalculated by the monitor, and an arterial oxygen saturation value isempirically determined based on the ratio obtained. The monitor containscircuitry for controlling the sensor, processing sensor signals anddisplaying a patient's oxygen saturation, heart rate andplethysmographic waveform. A pulse oximetry monitor is described in U.S.Pat. No. 5,632,272 assigned to the assignee of the present invention.

[0005] The patient cable provides conductors between a first connectorat one end, which mates to the sensor, and a second connector at theother end which mates to the monitor. The conductors relay the drivecurrents from the monitor to the sensor emitters and the photodiodedetector signals from the sensor to the monitor.

SUMMARY OF THE INVENTION

[0006] A drawback to conventional pulse oximetry systems is the lack ofstandardization of the sensor and the monitor. Unless the sensor and themonitor are manufactured by the same company, it is unlikely that thesetwo components can be connected as a functioning pulse oximetry system.This incompatibility is mainly due to physical configuration and signalparameter differences among both the sensors and the monitors. Sensorsdiffer primarily with respect to the configuration, drive requirementsand wavelength of the LEDs. Sensors also differ in the configuration andvalue of coding and calibration resistors used to identify, for example,sensor type or LED wavelength. Monitors differ primarily with respect tothe configuration and current limit of the LED driver; the amount ofpreamplifier gain applied to the photodiode detector signal; and themethod of reading and interpreting sensor coding and calibrationresistors. Further, the physical interface between sensors and monitors,such as connector types and pinouts, is also variable. Sensor andmonitor variations among various pulse oximetry systems are discussed indetail below with respect to FIGS. 1 through 3.

[0007]FIG. 1 depicts one type of sensor 100 and a corresponding monitor150 for one type of pulse oximetry system. For this particular sensor100, the red LED 110 and infrared LED 120 are connected back-to-back andin parallel. That is, the anode 112 of the red LED 110 is connected tothe cathode 124 of the infrared LED 120 and the anode 122 of theinfrared LED 120 is connected to the cathode 114 of the red LED 110.Also for this sensor 100, the photodiode detector 130 is configured sothat the photodiode leads 102, 104 are not in common with either of theLED leads 106, 108.

[0008] As shown in FIG. 1, the sensor 100 is also configured with acoding resistor 140 in parallel with the LEDs 110, 120. The codingresistor 140 is provided as an indicator that can be read by the monitor150, as described in pending U.S. patent application Ser. No.08/478,493, filed Jun. 7, 1995 and assigned to the assignee of thepresent application. The resistor 140 is used, for example, to indicatethe type of sensor 100. In other words, the value of the coding resistor140 can be selected to indicate that the sensor 100 is an adult probe, apediatric probe, a neonatal probe, a disposable probe or a reusableprobe. The coding resistor 140 is also utilized for security purposes.In other words, the value of the coding resistor 140 is used to indicatethat the sensor 100 is from an authorized sensor supplier. This permitscontrol over safety and performance concerns which arise withunauthorized sensors. In addition, the coding resistor 140 is used toindicate physical characteristics of the sensor 100, such as thewavelengths of the LEDs 110, 120.

[0009] Also shown in FIG. 1 is a portion of a monitor 150 that iscompatible with the sensor described above. The monitor 150 has drivecircuitry that includes a pair of current drivers 162, 164 and aswitching circuit 170. The monitor 150 also has a signal conditioner,which includes an input buffer 195 that conditions the output of thesensor photodiode 130. In addition, the monitor has a low-voltage source164 and corresponding reference resistor 194 that read the sensor codingresistor 140.

[0010] Each current driver 162, 164 provides one of the LEDs 110, 120with a predetermined activation current as controlled by the switchingcircuit 170. The switching circuit 170, functionally, is a double-pole,triple throw (2P3T) switch. A first switch 172 connects to a first LEDlead 106 and a second switch 174 connects to a second LED lead 108. Thefirst switch 172 has a first position 181 connected to the red LEDdriver 162; a second position 182 connected to a reference resistor 194and a buffer 195; and a third position 183 connected to ground 168. Thesecond switch 174 has a first position 181 connected to ground 168; asecond position 182 connected to a low-voltage source 192; and a thirdposition 183 connected to the infrared LED driver 164.

[0011] During a particular time interval, the switching circuit 170causes the first switch 172 to connect the red LED driver 162 to the redLED anode 112 and simultaneously causes the second switch 174 to connectthe ground 168 to the red LED cathode 114. As a result, a forwardcurrent is established in the red LED 110, which is activated to emitlight. During another particular time interval, the switching circuit170 causes the first switch 172 to connect the ground 168 to theinfrared LED cathode 124 and simultaneously causes the second switch 174to connect the infrared LED driver 164 to the infrared LED anode 122. Asa result, a forward current is established in the infrared LED, which isactivated to emit light. This cycle is repeated to cause the sensor toalternately emit red and infrared light. These alternating light pulsesresult in currents in the photodiode detector 130, which are input to amonitor buffer 166 and multiplexed 197 into an analog-to-digitalconverter (ADC) 199. The digitized outputs from the ADC 199,representing detected intensities, are then processed by the monitor 150and displayed as oxygen status.

[0012] During a monitor initialization interval, the switching circuit170 causes the first and second switches 172, 174 to be in a secondposition 182. This isolates the LED leads 106, 108 from the drivers 162,164 and ground 168. Further, the low-voltage source 192 is connected toone LED lead 108 and the reference resistor 194 is connected to theother LED lead 106. As a result, a voltage is established across theparallel combination of the coding resistor 140 and the LEDs 110, 120.If this voltage is less than the forward voltage of the forward biasedinfrared LED 120, then, because the red LED 110 is reverse biased,neither LED 110, 120 conducts significant current. In such a scenario,the current that passes through the parallel combination of the red LED110, infrared LED 120, and coding resistor 140 is approximately equal tothe current through the coding resistor 140. Thus, the equivalentcircuit is the low-voltage source 192 across the series combination ofthe coding resistor 140 and the reference resistor 194. The resistanceof the coding resistor 140 is then easily determined via Ohms Law fromthe voltage across the reference resistor 194, which is read as adigitized value from the ADC 154.

[0013]FIG. 2 depicts another type of sensor 200 and correspondingmonitor 250 for a conventional pulse oximetry system. This pulseoximetry system is described in U.S. Pat. No. 4,621,643 to New Jr. etal., issued Nov. 11, 1986. The sensor 200 of FIG. 2 is similar to thatof FIG. 1 in that it comprises a red LED 210 and an infrared LED 220.However, in this sensor 200, the LEDs 210, 220 are in a common cathode,three-wire configuration. That is, the cathode 214 of the red LED 210 isconnected to the cathode 224 of the infrared LED 220 and a common inputlead 208. Also, the anode 212 of the red LED 210 and the anode 222 ofthe infrared LED 220 have separate input leads 202, 204. The photodiodedetector 230 shown in FIG. 2 functions in much the same way as thedetector 130 shown in FIG. 1 but shares one input lead 208 with thesensor LEDs 210, 220. As shown in FIG. 2, the sensor 200 also has acalibration resistor 240 with one separate input lead 206 and one lead208 in common with the LEDs 210, 220 and photodiode 230. This resistor240 is encoded to correspond to the measured wavelength combination ofthe red LED 210 and infrared LED 220.

[0014] Also shown in FIG. 2 is a portion of a monitor 250 that iscompatible with the depicted sensor 200. The monitor 250 has LED drivecircuitry 260 which activates the LEDs 210, 220 one at time with apredetermined drive current independently applied to each of the LEDanodes 212, 222. The monitor 250 also has a signal conditioner,including amplification and filtration circuitry 270 that conditions theinput current from the detector 230, which is multiplexed 282 into asuccessive-approximation analog-to-digital converter (ADC) 284comprising a comparator 285 and digital-to-analog converter (DAC) 286. Amicroprocessor 288 then reads the digitized detector signal foranalysis. The monitor 250 reads the calibration resistor 240 by passinga predetermined current from a current source 290 through the resistor240. The microprocessor 288 reads the resulting voltage across theresistor 240, which is passed through the multiplexer 282 and ADC 284.The microprocessor 288 then computes the resistor value per Ohm's Law.

[0015]FIG. 3 illustrates yet another type of sensor 300 andcorresponding monitor 350. This configuration is similar to those ofFIGS. 1 and 2 in that the sensor 300 has a red LED 310, an infrared LED320 and a photodiode detector 330. The configuration of the LEDs 310,320 and the corresponding LED driver 360, however, differ from thosepreviously described. The LED driver 360 has a voltage source 362, a redLED current sink 364 and an infrared LED current sink 367. The LEDs 310,320 are arranged in a three-wire, common-anode configuration. That is,the red LED anode 312 and the infrared LED anode 322 have a common anodelead 302, the red LED cathode 314 has one separate lead 304 and theinfrared LED cathode 324 has another separate lead 305. The voltagesource output 352 connects to the common anode lead 302, the red LEDcurrent sink input 354 connects to the red LED cathode lead 304, and theinfrared LED current sink input 355 connects to the infrared LED cathodelead 305.

[0016] The current sinks 364, 367 control the drive current through eachLED 310, 320. The voltage source 362 has sufficient output capability tosupply this drive current to each LED 310, 320 individually. Eachcurrent sink 364, 367 is a grounded emitter transistor 365, 368 having abias resistor 366, 369 and a base control input 372, 374 that switcheseach transistor 365, 368 on and off. The bias resistor value and voltageof the base control input determine the amount of LED drive current. Inoperation, the red and infrared LEDs 310, 320 are alternately activatedby pulsed control signals alternately applied to the base control inputs372, 374.

[0017] The detector portion of the sensor 300 of FIG. 3 also differsfrom those in the previously miniature described sensors in that a gainresistor 340 is connected to the photodiode 330. When connected to thecorresponding monitor 350, the gain resistor 340 provides feedback,which adjusts the gain of a monitor preamplifier within the signalconditioner portion 380 of the monitor 350, which reduces thepreamplifier dynamic range requirements. For example, if the sensor 300is configured for neo-natal patients, where the sensor site is ofrelatively narrow thickness and the skin relatively transparent, thegain can be correspondingly low. However, if the sensor 300 isconfigured for adult patients, with a relatively thick and opaque sensorsite, such as a finger, the gain can be correspondingly higher tocompensate for lower detected intensities.

[0018]FIGS. 1 through 3 are examples of just some of the functionalvariations between sensors and monitors in pulse oximetry systems. Thesefunctional variations thwart the use of different sensors on differentmonitors. There are other sensor and monitor variations not describedabove. For example, a sensor may have LEDs with a three-wirecommon-anode configuration, as depicted in FIG. 7 below. There are alsoother potential mismatches between sensors and monitors. For example,the LED drive current supplied by a particular monitor may be either toohigh or too low for the LEDs on an incompatible sensor.

[0019] Besides the functional variations described above, physicalvariations between sensors and monitors may prevent interconnection toform a pulse oximetry system. For example, sensors have a variety ofconnectors. These connectors may vary from subminiature D-typeconnectors to flex-circuit edge connectors to name a few. Similarconnector variations exist on the monitor. Further, some pulse oximetrysystems require a separate patient cable, which mates to the sensor atone end and the monitor at the other end to span the distance betweenpatient and monitor. In other systems, the sensor incorporates a cablethat plugs directly into a monitor. Another physical variation is thepinouts at both the sensor connector and monitor connector. That is,there are potential differences between what signals are assigned towhat connector pins.

[0020] A conventional adapter cable can sometimes be used tointerconnect two dissimilar devices. The connector at one end of theadapter cable is configured to mate with one device and the connector atthe other end of the cable is configured to mate with the second device.The cable wires can be cross-connected as necessary to account forpinout differences. A conventional adapter cable, however, is of littleuse in interconnecting various sensors to various pulse oximetrymonitors. As described above, although the sensors have similarcomponents that perform similar functions, the incompatibilities aremore than connector and pinout related. In particular, a conventionaladapter cable is incapable of correcting for the signal mismatchesbetween sensors and monitors.

[0021] Although it is perhaps possible to design sensors thataccommodate a variety of monitors, such sensors would be, for the mostpart, commercially impractical. For one, pulse oximetry sensors can beeither reusable or disposable. In the case of disposable sensors, costper sensor is critical. Even for reusable sensors, cost and complexityare important design factors. A universal sensor having integratedadapter components could be significantly more expensive than thesensors described in FIGS. 1 through 3. A sensor adapter according tothe present invention solves many of the problems associated with bothsensor and monitor compatibility and the need to avoid sensorcomplexity.

[0022] One aspect of the present invention is an adapter that providesan interconnection between a pulse oximetry sensor and a monitor. Thesensor has a light source and a light detector, and the monitor has adriver and a signal conditioner. The adapter comprises a plurality ofsignal paths. The signal paths are detachably connected to either themonitor, the sensor or both. A first signal path is in communicationwith the driver and the light source. A second signal path is incommunication with the light detector and the signal conditioner. Theadapter also comprises an adapter element that is connected to at leastone of the signal paths. The adapter element modifies a characteristicof at least one of the signal paths so that the sensor and the monitorare jointly operable to measure oxygen status. In one embodiment, wherethe monitor has an information element detector in communication with atleast one of the signal paths, the adapter element conveys informationabout the sensor that is compatible with the information elementdetector. In another embodiment, the adapter element is connected to thefirst signal path and matches the light source configuration with thedriver configuration. In yet another embodiment, the adapter element isconnected to the first signal path and matches the drive requirements ofthe light source with the drive capabilities of the driver. In anadditional embodiment, the adapter element is connected to the secondsignal path and provides gain for a detector signal.

[0023] Another aspect of the present invention is a sensor adaptercomprising a sensor having a light source and a light detector andcomprising a plurality of signal paths. The signal paths are detachablyconnected to a monitor. A first signal path communicates a drive signalfrom the monitor to the light source. A second signal path communicatesan intensity signal from the light detector to the monitor. The sensoradapter also comprises an adapter element in communication with at leastone of the signal paths. The adapter element creates a compatibilitysignal that allows the sensor and the monitor to be jointly operable asa pulse oximetry system. In one embodiment, the sensor adapter comprisesan active component. The active component generates a predeterminedsignal level applied to the first signal path that conveys informationregarding a compatible sensor. In another embodiment of the sensoradapter, the light source has a conductive portion with a predeterminedequivalent resistance that conveys information regarding a compatiblesensor. Advantageously, the conductive portion may be an LED encapsulantor incorporated within the semiconductor material of an LED. In yetanother embodiment, the sensor adapter further comprises a translatorthat senses a sensor information element and communicates equivalentinformation to the monitor.

[0024] Yet another aspect of the present invention is a method ofconnecting an incompatible sensor to a monitor. The method comprises thestep of adapting a signal in communication with either the sensor, themonitor or both so that the sensor and the monitor are jointly operableas a pulse oximetry system. In one embodiment, the adapting stepcomprises the steps of sensing a drive signal and switching the drivesignal to a particular one of a plurality of light source leads inresponse to the drive signal. Advantageously, the switching step mayconnect a two-wire driver to a three-wire light source or may connect athree-wire driver to a two-wire light source, either connection beingmade through a multiple-pole, multiple-throw switch. In anotherembodiment, the adapting step comprises adjusting a drive signal fromthe monitor to match the drive requirements of a light source in thesensor. In yet another embodiment, the adapting step comprises providinga feedback signal to the monitor. The amount of the feedback determinesthe gain applied within the monitor to a light detector signal from thesensor. In an additional embodiment, the adapting step comprisesgenerating an information signal to an information element detector thatcorresponds to information from a compatible sensor. In anotherembodiment, the adapting step comprises translating an informationsignal from a sensor into a translated information signal that is readby an information element detector and corresponds to a compatiblesensor.

[0025] A further aspect of the present invention is a sensor adapter foroperably interconnecting an incompatible sensor to a monitor in a pulseoximetry system comprising an interconnect means for providing a signalpath between the sensor and the monitor. The sensor adapter alsocomprises an adapter means for creating a compatible signal on thesignal path. In one embodiment, the adapter means comprises aconfiguration means for routing a drive signal from the monitor so as tocorrespond to a light source in the sensor. In another embodiment, theadapter means comprises a limit means for changing the amount of a drivesignal from the monitor so as to correspond to a light source in thesensor. In yet another embodiment, the adapter means comprises a gainmeans for modifying the amplitude of a detector signal from the sensor.In an additional embodiment, the adapter means comprises an informationmeans for providing a signal to an information element detector thatcorresponds to a compatible sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention is described in detail below in connectionwith the following drawing figures in which:

[0027]FIG. 1 is a schematic diagram representing a sensor andcorresponding monitor interface circuitry;

[0028]FIG. 2 is a schematic diagram representing another prior artsensor and corresponding monitor interface circuitry;

[0029]FIG. 3 is a schematic diagram representing yet another prior artsensor and corresponding monitor interface circuitry;

[0030]FIG. 4 is a block diagram of a sensor adapter according to thepresent invention;

[0031]FIG. 5 is an illustration of various physical embodiments of asensor adapter in relation to a sensor and a monitor;

[0032]FIG. 6 is a block diagram of a drive configuration adapter portionof the sensor adapter for a monitor with three-wire, common-anodedrivers to a sensor with two-wire, back-to-back LEDs;

[0033]FIG. 7 is a block diagram of a drive configuration adapter portionof the sensor adapter for a monitor with two-wire, back-to-back LEDdrivers to a sensor with three-wire, common-anode LEDs;

[0034]FIG. 8 is a block diagram of a drive limit adapter portion of thesensor adapter illustrating a drive current gain;

[0035]FIG. 9 is a block diagram of a drive limit adapter portion of thesensor adapter illustrating a drive current reduction;

[0036]FIG. 10 is a block diagram illustrating the active gain adapterportion of the sensor adapter;

[0037]FIG. 11 is a schematic of an embodiment of the informationgenerator adapter portion of the sensor adapter featuring an adapterinformation element;

[0038]FIG. 12 is a schematic of another embodiment of the informationgenerator adapter portion of the sensor adapter;

[0039]FIG. 13 is a schematic of yet another embodiment of theinformation generator adapter portion of the sensor adapter;

[0040]FIG. 14 is a schematic diagram of the information translationadapter portion of the sensor adapter;

[0041]FIG. 15 is a block diagram of a universal sensor adapterembodiment of the sensor adapter;

[0042]FIG. 16 is an illustration of a universal adapter cable embodimentof the universal sensor adapter;

[0043]FIG. 17 is a block diagram of the configuration adapter portion ofthe universal sensor adapter; and

[0044]FIG. 18 is a schematic diagram of the driver test and sensor testportions of the configuration adapter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0045]FIG. 4 shows a functional block diagram of a sensor adapter 400for interconnecting a sensor 402 to an incompatible monitor 404 in apulse oximetry system. Interconnecting the monitor light source driver410 with the sensor light source 412 are a light source configuration414 adapter and a drive limit 418 adapter. The light sourceconfiguration 414 element adapts the light source driver 410 to theparticular configuration of the sensor light source 412, such astwo-wire, back-to-back LEDs, three-wire, common-anode LEDs andthree-wire, common-cathode LEDs. The drive limit 418 element increasesor decreases the current of the light source driver 410 to adapt to therequirements of the sensor light source 412.

[0046] Also shown in FIG. 4 is an active gain 434 element, which adaptsthe sensor light detector 432 to the monitor signal conditioner 430.Active gain 434 sets the amount of amplification of the signal from thesensor light detector 432 that occurs in the monitor signal conditioner430. Active gain 434 may also provide preamplification of the lightdetector signal before input to the monitor 404.

[0047]FIG. 4 further shows a monitor information element detector 450that is interconnected with an information generator 458 and informationtranslator 454. The information generator 458 simulates an informationelement 452 on the sensor to provide the monitor information elementdetector 450 with information regarding, for example, sensor type,origin or light source calibration. The information translator 454 readsa sensor information element 452 and provides the equivalent informationto the monitor information element detector 450, adapting to theconfiguration and value expected by the monitor 404.

[0048] As shown in FIG. 4, the sensor adapter 400 has a power supply470. As such, the functions of the sensor adapter 400 as described abovecan be performed with both active and passive components. In oneembodiment, the power supply 470 has an internal power source 472, suchas a lithium-ion battery. In another embodiment, the power supply 470uses an external power source. The external power source may be, forexample, one or more d.c. voltages available from a monitor output 474.Alternatively, the external power source may be derived from the lightsource driver 410, which supplies pulsed power to the sensor lightsource 412. A fraction of this pulsed power can be routed by a tap 478to the power supply 470, where it is a.c.-to-d.c. converted. Regardlessof the power source, the power supply 470 may also include d.c.-to-d.c.conversion, filtering and voltage regulation to provide suitable voltagelevels and power conditioning for the active components of the sensoradapter 400, as is well-known in the art.

[0049]FIG. 5 illustrates embodiments of the pulse oximetry sensoradapter according to the present invention. In one embodiment, thesensor adapter is configured as a connector block 510 that has a firstconnector 512 on one end that is attachable directly to a monitor 502 byplugging into a monitor connector 504 and a second connector 514 on theother end that accepts a cable connector 522. The components of thesensor adapter are mounted to a small substrate 515, and may be, forexample, surface-mount devices soldered on one or both sides of acircuit board or flex-circuit. The substrate 515 is electricallyinterconnected to the connectors 512, 514. This interconnection may bedone with conductors 516, such as individual wires, flex-circuit tracesor ribbon cable soldered to both the substrate 515 and the connectors512, 514. Alternatively, the substrate 515, might be directly attachedto both connectors 512, 514. The substrate 515, conductors 516 andportions of the connectors 512, 514 are encapsulated by insulatingmaterial that forms the connector block body 518. One will recognizeother possibilities for mounting and interconnecting the adaptercomponents within the connector block 510.

[0050]FIG. 5 illustrates another embodiment of the sensor adapter wherethe adapter is configured as an adapter cable 520 that also serves thefunction and substitutes for a conventional patient cable or sensorcable. In this embodiment, the sensor adapter can be alternativelyincorporated into a first end portion 530 of the cable 520, which wouldattach proximate to the monitor 502; a second end portion 540 of thecable 520, which would attach proximate to the sensor 506; or the cablebody 522, as, for example, an attached molded cable block 550. Whetherincorporated into the first end portion 530, second end portion 540 orthe cable body 522, the adapter components are mounted to a substrate515, as described.

[0051] If the sensor adapter is incorporated into the first end portion530 or the second end portion 540, the substrate 515 with the adaptercomponents is interconnected between the cable connector 522, 542 andthe wiring within the cable body 522. If the sensor adapter isincorporated into the cable body 522, the substrate 515 isinterconnected with the wiring within the cable body 522. Regardless,the substrate 515 is interconnected as described above with respect tothe connector block 510. The substrate 515, connector 522, 542 andinterconnection are then encapsulated to form a connector body 532, 542or cable block body 552, also as described above.

[0052] As shown in FIG. 5, the sensor adapter may also be incorporatedinto the sensor 506. This, however, increases the cost of the sensor,which may be particularly critical for disposable sensors. For thisembodiment, the adapter components can be mounted on a substrate 515, asdescribed above. In turn, the substrate 515 can be mounted to the sensor506, for example, by attaching and electrically interconnecting thesubstrate 515 to a flex circuit portion of the sensor 506.Alternatively, the adapter components can be mounted directly to theflex circuit portion of the sensor 506 or incorporated within particularsensor components, as with a conductive LED layer or encapsulant to forma coding or calibration resistor, as described below.

[0053]FIG. 6 shows an embodiment of the light source configurationportion 414 of the sensor adapter. The light source portion 412 of thesensor is shown with a red LED 110 and infrared LED 120 in aback-to-back configuration. The light source driver portion 410 of themonitor is shown with a voltage source 362 and two current sinks 364,367. This driver was described above with respect to FIG. 3 inconnection with a common-anode LED sensor. Thus, the embodiment of thelight source configuration element 414 shown in FIG. 6 adapts athree-wire common-anode driver to a two-wire, back-to-back LED lightsource. The discussion below is equally applicable to a sensor where thepositions of the red LED 110 and the infrared LED 120 are swapped and,correspondingly, that of the red LED current sink 364 and infrared LEDcurrent sink 367 are swapped from that shown in FIG. 6.

[0054] As shown in FIG. 6, the adapter 414 has a double-pole,double-throw (DPDT) switch 610. A first switch pole 612 is connected toa first lead 106 of the sensor LEDs 110, 120. A second switch pole 614is connected to a second lead 108 of the sensor LEDs 110, 120. In afirst position 616 (depicted), the switch 610 connects the red LED anode112 to the voltage source 362 and the red LED cathode 114 to the red LEDcurrent sink 364. In a second position 618 (not depicted), the switch610 connects the infrared LED anode 122 to the voltage source 362 andthe infrared LED cathode 124 to the infrared LED current sink 367. Inthis manner, the voltage source 362 is alternately switched between LEDanodes 112, 122 and the appropriate current sink 364, 367 is alternatelyswitched to the appropriate LED cathode 114, 124, alternately activatingeach of the LEDs 110,120.

[0055] As illustrated in FIG. 6, the adapter also has a drive sense 620that controls the switch 610. The drive sense 620 has a tap 652, 654,655 on each of the monitor driver leads 352, 354, 355, which allows thedrive sense 620 to determine which of the current sink transistors 365,368 is biased to a conducting state. The drive sense 620 then sets theswitch position accordingly. One will recognize many ways to implementthe drive sense 620. For example, the output of a differential amplifiercould control the switch 610, where the amplifier input is a resistorconnected between the voltage source 362 and the red LED current sink364. The amplifier could detect the voltage drop as current flows in theresistor when the red LED current sink 364 is in a conducting state, andactuate the switch 610 to the first position accordingly. When novoltage drop is detected, the switch 610 would return to the secondposition.

[0056] The switch 610 is implemented with active components, such asmultiple FET transistors connected in a DPDT configuration and having acontrol voltage applied to the FET gates to control conduction throughthe FET channels, as is well-known in the art. One will also recognizethat a number of FET transistor configurations are equivalent to theDPDT configuration shown in FIG. 6.

[0057]FIG. 7 shows another embodiment of the light source configurationportion 414 of the sensor adapter. The light source portion 412 of thesensor is shown with a red LED 310 and infrared LED 320 in a three-wire,common-anode configuration. The light source driver portion 410 of themonitor is shown with two drivers 162, 164 and a DPDT switch 170. Thisdriver was described above with respect to FIG. 1 in connection with aback-to-back LED sensor. Thus, the embodiment of the light sourceconfiguration element 414 shown in FIG. 7 adapts a two-wire,back-to-back LED driver 410 with a three-wire, common-anode LED lightsource 412.

[0058] As shown in FIG. 7, the adapter has a triple-pole, double-throw(3PDT) switch 710. A first switch pole 712 is connected to a first lead302 of the sensor LEDs 310, 320. A second switch pole 714 is connectedto a second lead 304 of the LEDs 310, 320. A third switch pole 718 isconnected to a third lead 305 of the LEDs 310, 320. The adapter switchfirst position 722 corresponds to the driver switch first position 181,as depicted in FIG. 7. The adapter switch second position 728corresponds to the driver switch third position 183. When the driverswitch 170 is in the second position 182, the adapter switch 710 can bein either position 722, 728. In the first position 722, the adapterswitch 710 connects the red LED anode 312 to a first monitor lead 156,when that lead 156 is connected to the red LED current source 162. Inthis first position 722, the switch 710 also connects the red LEDcathode 314 to a second monitor lead 158, when that lead 158 isconnected to ground 168. In this first position 722, the infrared LEDcathode 324 is disconnected. In a second position 728, the adapterswitch 710 connects the infrared LED anode 322 to the monitor secondlead 158, when that lead 158 is connected to the infrared LED currentsource 164. In this second position 728, the adapter switch 710 alsoconnects the infrared LED cathode 324 to the first monitor lead 156,when that lead 156 is connected to ground 168. In this second position728, the red LED cathode 314 is disconnected. In this manner, the redLED current source 162 is driving the red LED 310 alternately as theinfrared LED current source 164 is driving the infrared LED 320.

[0059] As illustrated in FIG. 7, the light source configuration portion414 of the sensor adapter also has a drive sense 730 that controls thepositions of the adapter switch 710. The drive sense 730 has a tap 756,758 on each of the driver leads 156, 158 that allow the drive sense 730to determine the position of the driver switch 170. The drive sense 730then sets the sensor switch position accordingly. One will recognizemany ways to implement the drive sense 730. For example, a differentialamplifier could detect the polarity of the taps 756, 758, the amplifieroutput controlling the positions of the adapter switch 710. For example,the amplifier could detect that the polarity of the first monitor lead156 is positive with respect to the second monitor lead 158, indicatingthe driver switch 170 is in the first position 181. The amplifier outputwould then actuate the adapter switch 710 to the first position 722. Asdiscussed above with respect to FIG. 6, the switch is implemented withactive components, for example, FET transistors. Also, as discussedabove, one will also recognize that a number of FET transistorconfigurations would be equivalent to the 3PDT configuration shown inFIG. 7.

[0060]FIG. 8 shows an embodiment of the drive limit portion 418 of thesensor adapter. In this embodiment, the drive limit adapter 418 providesincreased drive current through the sensor light source 410. Forpurposes of illustration, the sensor light source 410 shown in FIG. 8 isa three-wire, common-anode LED configuration as described above withrespect to FIG. 3. Also for purposes of illustration, the monitor lightsource driver 412 is configured to drive a three-wire, common-anode LEDconfiguration, also as described above with respect to FIG. 3. It isassumed, however, that the sensor LEDs 310, 320 require an increaseddrive current over what the driver 412 provides. The drive limit adapterportion 418, therefore, provides an adapter red LED current sink 810 inparallel with the monitor red LED current sink 364 and an adapterinfrared LED current sink 820 in parallel with the monitor infrared LEDcurrent sink 367. A drive sense 830 similar to the one described abovewith respect to FIG. 6 controls the adapter current sinks 810, 820. Thatis, the drive sense 830 has a tap 852, 854, 855 on each of the driverleads 352, 354, 355 that allow the drive sense 830 to determine which ofthe monitor current sinks 364, 367 are biased to a conducting state. Thedrive sense 830 then biases the corresponding adapter current sink 810,820 to a conducting state. The bias resistors 812, 822 and the biasvoltage applied by the drive sense control outputs 832, 834 determinethe current through the adapter current sinks 810, 820. The currentthrough the red LED 310 is the sum of the current through thecorresponding adapter red LED current sink 810 and the monitor redcurrent sink 364. Likewise, the current through the infrared LED 320 isthe sum of the current through the corresponding adapter infrared LEDcurrent sink 820 and the monitor infrared current sink 367.

[0061]FIG. 9 shows another embodiment of the drive limit portion 418 ofthe sensor adapter. In this embodiment, the drive limit adapter 418provides for decreased drive current through the sensor light source410. For purposes of illustration, the sensor light source 410 and themonitor driver 412 are shown the same as described above with respect toFIG. 8. For this embodiment, however, it is assumed that the sensor LEDs310, 320 require a reduced drive current from what the driver 412provides. The drive limit adapter 418, therefore, provides a red LEDshunt 910 and an infrared LED shunt 920. Each shunt 910, 920 allows anamount of current to bypass a particular LED 310, 320, as determined bythe resistance value of the shunt 910, 920. The current through the redLED 310 is the difference between the current drawn by the red LEDcurrent sink 364 and the current bypassed through the red LED shunt 910.Likewise, the current through the infrared LED 320 is the differencebetween the current drawn by the infrared LED current sink 367 and thecurrent bypassed through the infrared LED shunt 920.

[0062]FIG. 10 depicts an embodiment of the active gain portion 434 ofthe sensor adapter. Active gain 434 adapts the light detector portion432 of the sensor to the signal conditioner portion 430 of the monitor.One function of the active gain adapter 434 is to provide a resistor1080 in the feedback path 356 of a preamplifier 380, for monitors whichrequire this feature to control dynamic range, as described above withrespect to FIG. 3. The value, R_(gain), of the resistor 1080 determinesthe gain of the preamplifier 380. As illustrated in FIG. 10, anotherfunction of the active gain adapter 434 is to adjust the signal level ofthe photodiode 130. This function also adapts the dynamic range of themonitor preamplifier 380 to a particular sensor type or application. Avariable gain amplifier 1010 adjusts the detected signal level from thephotodiode 130. The amplifier inputs 1012, 1014 are connected to thephotodiode output leads 102, 104. The amplifier output 1018 drives thepreamplifier input 358. A single-pole, double-throw (SPDT) gain switch1060 selects one of two feedback resistors 1072, 1074. The selectedresistor value, R_(high) or R_(low), determines the amplifier gain.

[0063] The gain switch 1060 is controlled by a comparator 1020 incombination with a peak detector 1030 and a reference 1040. The peakdetector 1030 has an input 1032 connected to the output 1018 of theamplifier 1010. The peak detector 1030 measures the amplified differencebetween detector dark current and detector signal current. Thisdifference at the peak detector output 1034 is compared 1020 to areference output 1042. If the peak signal level is below the referencevalue, the comparator output 1022 actuates the gain switch 1060 toselect the high gain resistor 1072. If the peak signal level is abovethe reference value, the comparator output 1022 actuates the gain switch1060 to select the low gain resistor 1074. Hysteresis or integration ofthe peak detector output, for example, can be used to stabilize theamplifier gain settings, as is well-known in the art. Also, one willrecognize that a bank of N resistors and single-pole, N-throw switch canbe used to provide multiple gain settings for the amplifier 1010, asdetermined by multiple reference outputs from the reference source 1040.

[0064]FIG. 11 illustrates an embodiment of the information generatorportion 458 of the sensor adapter. An information element 1110 islocated in the sensor adapter to substitute for an equivalent sensorinformation element. The information element 1110 connects viaconductors 1120 to the information element detector portion 450 of themonitor 404, which senses the information content of the informationelement 1110. The information element 1110 may have series connections1130 or parallel connections 1140 to outputs 424 of the sensor 402.

[0065] As an example, the sensor adapter could be an adapter cablehaving a coding or calibration resistor mounted as described above withrespect to FIG. 5. In particular, as illustrated with the monitor 250 ofFIG. 2, the adapter cable could have an information element that is acalibration resistor, which connects between the monitor leads 256, 258.Similarly, as illustrated with the monitor 150 of FIG. 1, the adaptercable could have an information element that is a coding resistor, whichconnects between the monitor leads 156, 158. In this manner, a sensorwithout a coding or calibration resistor would properly function whenattached with the adapter cable to a monitor that requires such aresistor.

[0066] As illustrated in FIG. 1, an equivalent substitute for acalibration or coding resistor can also be located on the sensor itselfin the form of leakage resistance built into the sensor. In oneembodiment, the red LED 110 and infrared LED 120 can be encapsulatedwith a material having some conductance so as to form an equivalentresistance equal to the desired value of the coding resistor 140. Inanother embodiment, the semiconductor material of the red LED 110, theinfrared LED 120 or both can be fabricated with some conductance to forman equivalent resistance equal to the desired value of the codingresistor 140.

[0067]FIG. 12 illustrates another embodiment of the informationgenerator portion 458 of the sensor adapter. The information generator458 has a DPDT adapter switch 1210, an adapter resistor 1220 and alow-voltage detector 1230. The adapter switch 1210 has a first position1242 that connects the sensor LED leads 106, 108 to the monitor outputleads 156, 158. The adapter switch 1210 has a second position 1244 thatconnects the adapter resistor 1220 across the output leads 156, 158. Thelow-voltage detector 1230 has an input 1232 that can be connected to thelow-voltage output lead 158. The low-voltage detector 1230 has an outputthat controls the adapter switch 1210.

[0068] As illustrated in FIG. 12, the operation of the informationgenerator 458 is illustrated with respect to the monitor 150, describedabove with respect to FIG. 1. In its first position 1242, the adapterswitch 1210 connects the two leads of the sensor LEDs 106, 108 to thetwo monitor output leads 156, 158. The adapter switch first position1242 corresponds to the monitor switching circuit first position 181 andthird position 183, at which the LED drivers 162, 164 alternatelyactivate the LEDs 110, 120.

[0069] As shown in FIG. 12 and described above with respect to FIG. 1,during calibration, the switching circuit 170 is set to a secondposition 182 which isolates the monitor output leads 156, 158 from thedrivers 162, 164 and ground 168. During this calibration period, acombination of a low-voltage source 192 and a reference resistor 194 areconnected to the output leads 156, 158 to determine the value of asensor coding resistor. The low voltage detector 1230 senses the lowvoltage on the output leads 156 and actuates the adapter switch 1210 toits second position 1244. With the adapter switch 1210 in the secondposition 1244, the adapter resistor 1220 is connected between to thelow-voltage source 192 and the reference resistor 194. As a result, themonitor reads the value of the adapter resistor 1220, which is apredetermined resistance equivalent to the value of a coding resistorrequired by the monitor 150 for proper operation. In this manner, theinformation generator 458 adapts a sensor 100 without a coding resistor140 to the monitor 150.

[0070]FIG. 13 illustrates yet another embodiment of the informationgenerator portion 458 of the sensor adapter. The information generator458 comprises a fixed voltage source 1310 connected to the output lead156 of the reference resistor 194. The voltage source 1310 has a biasvoltage input 1312 and, bias resistors 1314, which divide the voltagebetween the bias voltage input 1312 and the input 1315 of the bufferamplifier 1316. The output 1317 of the amplifier 1316 is connected tothe anode of an isolation diode 1318, the cathode of which is connectedto the output lead 156. While the LEDs 110, 120 are driven, theisolation diode 1318 is back biased by the red LED driver 162 or by thecombination of the infrared LED driver 164 and the infrared LED 120voltage drop, effectively isolating the fixed voltage source 1310 fromthe output lead 156.

[0071] During the initialization interval described above, the monitor150 is expecting to read a coding resistor of value

R _(c) =R _(ref)[(V _(low) /V _(adc))−1],

[0072] where R_(ref) is the resistance of the monitor reference resistor194, V_(low) is the output voltage of the low-voltage source 192 andV_(adc) is the voltage measured at the buffer input 196 and also outputto the ADC 199. The LEDs 110, 120 are not conducting during thecalibration period because the red LED 110 is back biased and thelow-voltage source 192 provides insufficient forward voltage to theinfrared LED 120 for conduction to occur. Because the sensor 100 doesnot have a coding resistor, the low-voltage source 192 is effectivelyisolated from the output lead 156 and reference resistor 194. Duringthis period, the isolation diode 1318 is forward biased by the amplifier1317. As a result, the voltage at the amplifier output 1317, ignoringthe diode voltage drop, appears across the reference resistor 194. Ifthe predetermined value of the voltage source is

V=V _(low) [R _(ref)/(R _(c) +R _(ref))],

[0073] The voltage at the buffer input 196 is the same as if the sensorhad a coding resistor of value, R_(c), as can be seen by substituting Vfor V_(adc) in the equation for R_(c) above. Thus, the fixed voltagesource provides equivalent information to the monitor 150 as if thesensor 100 had a coding resistor. One will recognize that other voltagesource configurations are possible. Further, an equivalent currentsource can be connected to the output lead 156 to simulate a sensorcoding resistor. The predetermined value of that current source is:

I=V _(low)/(R _(c) +R _(ref))

[0074] This current flows through the reference resistor 194 such thatthe voltage read by the monitor, V_(adc) at the ADC 199, is the same asgiven above for the voltage source embodiment.

[0075]FIG. 14 illustrates an embodiment of the information translatorportion 454 of the sensor adapter. The information translator 454 readsa sensor information element 452 and provides an equivalent value, i.e.a translated value providing the same information, to the informationelement detector portion 450 of a monitor 404. The translator 454 has aninformation element reader 1410 that determines the sensor information,e.g. sensor type, manufacturer, calibration data, or security code froma sensor information element 452. The translator 454 also has aninformation element array 1420. The array 1420 is a predetermined set ofdifferent information elements that correspond to the possible sensorsthat the monitor 404 accepts. At least one information element isselected from the array 1420 and connected to the information elementdetector 450, as determined by a switching circuit 1430. The informationelement reader 1410 controls the state of the switching circuit 1430. Inthis manner, the information element reader 1410 can determine thesensor information element value, select an equivalent value from theinformation element array 1420, and actuate the switching circuit 1430,thereby connecting the corresponding element or elements from the array1420 to the monitor information element detector 450.

[0076]FIG. 15 shows an embodiment of a sensor adapter which incorporatesa combination of the adapter elements described above in addition toother elements described in detail below to create a universal adapter1500. In general, the universal adapter 1500 allows one sensor 1502 froma variety of possible sensors to be connected to one monitor 1504 from avariety of possible monitors to create a pulse oximetry system. Theuniversal adapter 1500 has a first connector adapter 1510, a monitorselector 1520, a first switch 1530 and a number of adapter elements1540. These components allow the universal adapter 1500 to sense theelectrical characteristics of the monitor 1504, such as the driveconfiguration and drive levels, and to select the necessary adapterelements 1540 accordingly. The universal adapter 1500 also has a secondconnector adapter 1560, a sensor selector 1570, and a second switch1580. These components allow the universal adapter to sense theelectrical characteristics of the sensor 1502, such as LED configurationand information element presence and to select the necessary adapterelements 1540 accordingly.

[0077]FIG. 16 further illustrates the universal adapter 1500 describedabove with respect to FIG. 15. The universal adapter 1500 is shown as asensor adapter cable 1600 having generic connectors 1610, 1620 at eitherend of the cable 1600. Attached to the cable and electrically connectedto the cable wiring is an molded cable block 550 as described above withrespect to FIG. 5. The cable block contains the adapter components 1520,1530, 1540, 1570, 1580 shown in FIG. 15.

[0078] As illustrated in FIG. 16, a first connector adapter 1510 is aconventional adapter cable having a connector 1630 at one end whichmates with the generic connector 1620 of the sensor adapter cable 1600.A connector 1640 at the other end of the connector adapter 1510 is thespecific connector which mates with a particular monitor connector 1650.The cable wiring of the connector adapter 1510 is cross-wired betweenthe end connectors 1630, 1640 as necessary to match the predeterminedpinouts of the connector 1620 of the sensor adapter cable 1600 to thepinouts of the connector 1650 of the monitor 1504. In this manner, thefirst connector adapter 1510 accommodates a variety of physicalconnectors and pinouts of various monitors 1504.

[0079] Likewise, a second connector adapter 1560 is a conventionaladapter cable having a connector 1660 at one end which mates with thegeneric connector 1610 of the sensor adapter cable 1600. A connector1670 at the other end of the connector adapter 1560 is the specificconnector 1670 which mates with a particular sensor connector 1680. Thecable wiring of the connector adapter 1560 is cross-wired between theend connectors 1660, 1670 as necessary to match the predeterminedpinouts of the connector 1610 of the sensor adapter cable 1500 to thepinouts of the connector 1680 of the sensor 1502. In this manner, thesecond connector adapter 1560 accommodates a variety of physicalconnectors and pinouts of various sensors 1502. The sensor adapter cable1600, as described above, is advantageously of a single design havinggeneric connectors 1610, 1620 with predetermined signal pinouts thatmate with each of a family of specific adapter cables 1510, 1560manufactured to match specific sensors 1502 and specific monitors 1504.

[0080] As illustrated in FIG. 15, the signal lines 1532 between thefirst switch 1530 and the connector adapter 1510 have branches 1522 tothe monitor selector 1520. Because the pinouts of the universal adapter1500 are predetermined, it is known which of these signal lines 1532correspond to particular monitor leads 1512. Thus, the monitor selector1520 tests these signal lines 1532 to determine the signalcharacteristics of an attached monitor 1504, as described in more detailbelow with respect to FIG. 17. Once the signal characteristics for themonitor 1504 are determined, the output 1524 of the monitor selector1520 controls the first switch 1530 to connect the signal lines 1532 tocorresponding adapter element 1540.

[0081] Likewise, the signal lines 1582 between the second switch 1580and the connector adapter 1560 have branches 1572 to the sensor selector1570. Because the pinouts of the universal adapter 1500 arepredetermined, it is known which of these signal lines 1582 correspondto particular sensor leads 1562. Thus, the sensor selector 1570 teststhese signal lines 1582 to determine the signal characteristics of anattached sensor 1502, as described in more detail below with respect toFIG. 17. Once the signal characteristics for the sensor 1502 aredetermined, the output 1574 of the sensor selector 1570 controls thesecond switch 1580 to connect the signal lines 1582 to correspondingones of the adapter elements 1540.

[0082]FIG. 17 illustrates an embodiment for a configuration portion 1700of the universal adapter 1500 that matches the monitor driver 1704 tothe sensor LEDs 1702. This configuration portion 1700 has a driver test1710 and a switch control 1712. The driver test 1710 senses the driverconfiguration from the monitor signal lines 1532 and provides an output1714 to the switch control 1712. The switch control 1712 has inputs fromthe driver test output 1714 and the LED test output 1724 and provides acontrol output 1718 that causes a first bi-directional switch 1530 toconnect the monitor driver 1704 to the corresponding adapter elements1731-1737. That is, the first switch is equivalent to a bi-directionalone-line to seven-line multiplexer.

[0083] The configuration portion 1700 also has an LED test 1720. The LEDtest 1720 senses the LED configuration from the sensor signal lines 1582and provides an output 1724 to the switch control 1712. The switchcontrol 1712 has inputs from the LED test output 1724 and the drivertest output 1714 and provides a control output 1728 that causes a secondbi-directional switch 1580 to connect the sensor LEDs 1702 to thecorresponding adapter elements 1731-1737. The second switch 1580 isequivalent to the first switch 1530. The adapter elements compriseadapters 1732-1737 for all six combinations of drivers and incompatiblesensor configurations. In addition, there is a “straight-through”adapter 1731 for the case of matching drivers and sensor LEDs, e.g.back-to-back driver 1704 and back-to-back LEDs 1702.

[0084] As illustrated in FIG. 17, it is assumed that a monitor 1504 hasthree possible drivers 1704. That is, an attached monitor will havecircuitry for driving either back-to-back LEDs, common-anode LEDs orcommon-cathode LEDs. Thus, the configuration adapter 1700 has threesignal lines 1532 from the monitor driver 1704. For example, asillustrated in FIG. 6, a common-anode driver 410 has three leads 352,354, 355 that correspond to the three signal lines 1532. As illustratedin FIG. 7 as another example, a back-to-back driver 410 has two leads156, 158 which would correspond to two of the three signal lines 1532,leaving one of the three signal lines 1532 unused.

[0085]FIG. 18 illustrates an embodiment of the driver test 1710. Thedriver test 1710 looks at the three signal lines 1532 to determine thedriver configuration. The drive test circuit 1710 shown has threedifferential amplifiers 1810, 1820, 1830, each with inputs across aunique pair of the three signal lines 1532. That is, a first amplifier1810 senses a signal on a first pair of signal lines 1802, 1804, asecond amplifier 1820 senses a signal on a second pair of signal lines1802, 1805, and a third amplifier 1830 senses a signal on a third pairof signal lines 1804, 1805.

[0086] If a monitor driver is configured for back-to-back LEDs, then, asillustrated in FIG. 7, the equivalent to driver leads 156, 158 are wiredto correspond to signal lines 1802, 1804 shown in FIG. 18, respectively,and signal line 1805 is disconnected. The first amplifier 1810 wouldsense a voltage of alternating polarity corresponding to red LED andinfrared LED drive signals, and the second amplifier 1820 and thirdamplifier 1830 would sense nothing. Hence, an alternating output voltagefrom only the first amplifier 1810 would indicate to the switch control1712 in FIG. 17 that the driver 1704 is configured for back-to-backLEDs.

[0087] As illustrated in FIG. 18, by contrast, if the monitor driver isconfigured for common-anode LEDs, then, as illustrated in FIG. 6, theequivalent to driver leads 352, 354, 355 are wired to correspond tosignal lines 1802, 1804, 1805, shown in FIG. 18, respectively. The firstamplifier 1810 would sense a unipolar voltage corresponding to the redLED drive signal. The second amplifier 1820 would sense a unipolarvoltage corresponding to the infrared LED drive signal. The thirdamplifier 1830 would sense nothing. Hence, alternating output voltagesfrom the first amplifier 1810 and the second amplifier 1820 wouldindicate to the switch control 1712 in FIG. 17 that the driver 1704 isconfigured for common-cathode LEDs. By comparison, if the monitor driveris configured for common cathode LEDs, a different two of the amplifiers1810, 1820, 1830 would sense similar voltages as in the common-anodecase. Thus, the outputs of the amplifiers 1810, 1820, 1830 providesufficient information to the first switch control 1712 in FIG. 17 todetermine the driver configuration.

[0088] As illustrated in FIG. 17, it is assumed that a sensor 1502 hasthree possible LED configurations 1702. That is, an attached sensor willhave either back-to-back LEDs, common-anode LEDs or common-cathode LEDs.Thus, the configuration adapter 1700 has three signal lines 1582 fromthe sensor LEDs 1702. For example, as illustrated in FIG. 6, aback-to-back LED sensor 412 has two leads 106, 108 that correspond totwo of the three signal lines 1582, leaving one of the three signallines 1582 unused. As illustrated in FIG. 7 as another example, acommon-anode sensor 412 has three leads 302, 304, 305 that correspond tothe three signal lines 1582.

[0089]FIG. 18 illustrates an embodiment of the LED test 1720. The LEDtest 1720 looks at the three signal lines 1582 to determine the sensorconfiguration. The LED test circuit 1720 shown has a voltage source 1850and two differential amplifiers 1860, 1870 that provide a return pathfor the voltage source 1850. To test the sensor LED configuration, aswitch 1880 alternately connects the voltage source 1850 to each of thethree signal lines 1582 and, at the same time, connects the differentialamplifiers 1860, 1870 to the remaining two signal lines 1582. Forexample, in a first position 1882 (depicted), the output of the voltagesource 1850 is connected to a first signal line 1806, the input of thefirst amplifier 1860 is connected to a second signal line 1808, and theinput of the second amplifier 1870 is connected to a third signal line1809.

[0090] If a sensor has back-to-back LEDs, then, as illustrated in FIG.6, the equivalent to sensor leads 106, 108 are wired to correspond tosignal lines 1806, 1808 shown in FIG. 18, respectively, and signal line1809 is disconnected. In the first switch position 1882, the voltagesource 1850 drives the red LED and current is detected by the firstamplifier 1860. In the second position 1884, the voltage source 1850drives the infrared LED and current is detected by the first amplifier1860. In the third switch position 1886, the voltage source 1850 drivesthe disconnected line 1809 and no current is detected by eitheramplifier 1860, 1870. Hence, a voltage output from the first amplifier1860 at the first and second switch positions 1882, 1884, with noamplifier output at the third switch position 1886, indicates that thesensor has back-to-back LEDs.

[0091] As illustrated in FIG. 18, by contrast, if the sensor isconfigured for common-anode LEDs, then, as illustrated in FIG. 7, theequivalent to driver leads 302, 304, 305 are wired to correspond tosignal lines 1806, 1808, 1809, shown in FIG. 18, respectively. In thefirst switch position 1882, the voltage source 1850 drives the anodes ofboth LEDs, but a current path is only provided by the input to the firstamplifier 1860, which produces a corresponding output. In the second andthird switch positions 1884, 1886 the voltage source 1850 back biasesboth LEDs and no current is detected by either amplifier 1860, 1870.Hence, a voltage output from the first amplifier 1860 at the firstswitch position 1882, with no amplifier outputs at the second and thirdswitch positions 1884, 1886, indicates that the sensor has common-anodeLEDs. By comparison, if the sensor has common-cathode LEDs, in the firstswitch position 1882, the voltage source 1850 would back-bias the diodesand no current would be detected by either amplifier 1860, 1870. In thesecond and third positions 1884, 1886, current would be detected by thefirst and second amplifiers 1860, 1870, respectively. Thus, the outputsof the amplifiers 1860, 1870 provide sufficient information to thesecond switch control 1722 in FIG. 17 to determine the sensor LEDconfiguration.

[0092] As illustrated in FIG. 17, the switch control 1712 could be asimple state machine. After the LED test 1720 cycles through the threepositions of the switch 1880 shown in FIG. 18, and after the driver test1710 senses driver activation, the switch control 1712 would latch thefirst and second bi-direction switches 1530, 1580 to connect theappropriate adapter element to the signal lines 1532, 1582. For example,if back-to-back LEDs 1702 were detected and a common-anode driver 1704was detected, the bi-directional switches 1530, 1580 would connect thethree signal lines 1532, 1582 to the common-anode (CA) to back-to-back(BB) adapter element 1734. The CA to BB adapter element is describedabove with respect to FIG. 6.

[0093] As illustrated in FIG. 15, a simplified embodiment of theuniversal adapter 1500 is possible if the sensor 1502 is of a knownconfiguration. For example, a sensor manufacturer may wish to provide auniversal adapter 1500 between their particular sensors and most or allpulse oximetry monitors. In that case, there would be fewer combinationsof adapter elements 1540 and the first switch 1530 and second switch1580 would be simpler accordingly. For example, as illustrated in FIG.17, if it is known that the sensor 1502 has back-to-back LEDs 1702, thenonly the “straight-through” 1731, “CA to BB” 1734 and “CC to BB” 1736adapter elements are required. Correspondingly, the first switch 1530and second switch 1580 would be equivalent to bi-directional one-line tothree-line multiplexers, rather than the more complex one-line toseven-line multiplexers shown.

[0094] One would appreciate that testing and switching circuitry, suchas shown in FIG. 17, is also applicable to embodiments of, for example,drive limit portions and information translator portions of theuniversal adapter 1500 shown in FIG. 15. Further, one will recognizedthat portions of the sensor adapter shown in FIGS. 4 and 15 could beimplemented with microcontroller or microprocessor circuitry andassociated firmware rather than in hardwired circuitry. Also, particularadapter elements might be selected manually, such as with hand-actuatedswitches, rather than through automatic sensing of the sensor andmonitor configurations as described above. As another alternative toautomatic sensing of the sensor and monitor configurations, particularconnector adapters 1560, 1510 could contain coding elements thatfunction as indicators of the corresponding sensor 1502 or monitor 1504configurations.

[0095] The pulse oximetry sensor adapter has been disclosed in detail inconnection with the preferred embodiments of the present invention.These embodiments are disclosed by way of examples only and are not tolimit the scope of the present invention, which is defined by the claimsthat follow. One in the art will appreciate many variations andmodifications within the scope of this invention.

What is claimed is:
 1. A device configured to provide information to apulse oximetry monitor, said device comprising an information generatorconfigured to simulate information expected by the pulse oximetrymonitor, wherein the simulated information is provided to the pulseoximetry monitor on a first signal path in common with a second signalpath for communicating a driving signal from the pulse oximetry monitor.2. The device of claim 1, wherein the device is a sensor.
 3. The deviceof claim 1, wherein the device is an adapter configured to interconnectthe pulse oximetry monitor with a sensor.
 4. The device of claim 1,wherein the device is a cable configured to provide an interconnectionbetween the pulse oximetry monitor and a sensor.
 5. The device of claim1, wherein the simulated information indicates a sensor type to thepulse oximetry monitor.
 6. The device of claim 1, wherein the simulatedinformation indicates an operating wavelength.
 7. A device configured toprovide information to a pulse oximetry monitor, said device comprisingan information generator configured to simulate information expected bythe pulse oximetry monitor, wherein the simulated information isprovided to the pulse oximetry monitor on a first signal line in commonwith a second signal line for communicating an intensity signal to thepulse oximetry monitor.
 8. The device of claim 7, wherein the device isa sensor adapter.
 9. The device of claim 7, wherein the device is acombination of a sensor and an adapter.
 10. The device of claim 7,wherein the device is a connector.
 11. The device of claim 7, whereinthe simulated information conveys a characteristic of a sensor.
 12. Thedevice of claim 7, wherein the simulated information indicates source ofa sensor.
 13. A method of communicating expected information regarding asensor to an oximeter monitor, the method comprising: simulating theexpected information; and providing the expected information to theoximeter monitor on a first signal line in common with a second signalline for making measurements.
 14. The method of claim 13, wherein theexpected information relates to a sensor type which is compatible withthe oximeter monitor.
 15. The method of claim 13, wherein the sensorlacks the expected information.